<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>

</head>
<body>
    <dl id ="app">
        <dt>Java</dt>
        <dd>JavaSE</dd>
        <dd>JavaEE</dd>
        <dd>JavaME</dd>
    </dl>
    //要写在dl的下面
    <script>
        var dl = document.getElementById('app');
    </script>
</body>
</html>